The 97-cent trade that still needs two fills

Everyone loves this line: buy both sides for less than a dollar, then collect a dollar. The arithmetic is neat. The execution is where things get interesting.

Imagine a binary market with an executable YES ask of 48 cents and a NO ask of 49 cents. One matched pair costs 97 cents before costs. If the contract resolves normally to one winning outcome, that complete pair pays a dollar. This is a hypothetical example, not a live opportunity.

The awkward middle

Your first order fills. The other quote disappears. You now hold a directional position, not a complete pair. Buying the missing leg at 55 cents changes the entire trade.

A bot needs a plan for that moment: maximum combined cost, maximum unmatched inventory, and a timeout. A dashboard showing two attractive prices is only the beginning.

Count what actually happened

Record the quantity filled on each side, average entry price, fees, cancellation results, and any remaining exposure. Use the smaller filled quantity to count complete pairs. Keep the leftover shares separate.

Capital also stays tied up until you close, merge where available, or redeem after resolution. Three cents over several weeks is a different proposition from three cents over several minutes.

The useful question is whether both legs can be completed at the intended size. Start there. The profit calculation comes after the fills.

Further reading: Prices and order books · Resolution rules · Current fees.

Explore the markets: Open Polymarket (referral link).